1. Field of the Invention
This invention relates to means for sealing hose fittings and more particularly to means which lubricate and seal fittings to hoses carrying gases which are difficult to seal.
2. Description of the Prior Art
It has been found that certain gases and vapors, such as hydrogen, helium, fuel gas, and various halogenated refrigerants sometimes known by the trademark "Freon", are difficult to convey through hoses without substantial loss since they have a strong tendency to permeate through the wall of the hose. This is particularly true of hoses having synthetic rubber core tubes. This problem of leakage through the hose wall itself is largely overcome by core tubes made of a thermoplastic material which has a much greater sealing ability than synthetic rubber. The use of a thermoplastic for the core tube may create another problem when the hose is connected to reusable screw-together fittings since the relatively unyielding core tube material tends to incompletely fill the nipple threads in the fitting leaving a minute but continuous helical leakage path between the nipple and the core tube. Because of this, in a thermoplastic hose assembly practically all of the advantage of better sealing ability of the hose wall is lost due to leakage at the fittings.
A possible solution to this problem of leakage at the fittings is to eliminate the threaded connection by using permanently attached fittings having annular grooves creating leakage barriers at the points of contact between the nipple and the core tube. Such an approach, however, prevents the fittings from being attached without special tooling or being reused. Alternatively, a heavy bodied sealant might be used. The sealant, however, tends to lose its effectiveness after flexing or temperature cycling, and from reduction or elimination of the compression upon the sealant.
Because hoses having thermoplastic core tubes are so very effective in preventing the passage of gas through their walls, but so much less effective in forming a good seal between the core tube and a screw-together reusable fitting, it has become desirable to develop a means for securing the fitting to the thermoplastic core tube to prevent leakage therebetween while allowing the fitting to be reused.